What to do with leftover lamb ( other than pita sandwichs.. Did those already)?

Shepherd's pie is a nice option. Especially if you have a lot of it.

My family likes to thinly slice it and use it in fajitas. We just gently reheat it on the stovetop.

I don't like it reheated, so I use it in salads. One of my favorites is pretty simple: mixed lettuces, Feta cheese, Kalamata olives, cucumber slices, some red onion, with an lemon & orange vinaigrette (including some zest). And some sliced lamb.